Interlayer interactions in anisotropic atomically thin rhenium diselenide

In this work, we study the interlayer phonon vibration modes, the layer-number- dependent optical bandgap, and the anisotropic photoluminescence （PL） spectra of atomically thin rhenium diselenide （ReSe2） for the first time. The ultralow frequency interlayer Raman spectra and the polarization-resolved high frequency Raman spectra in ReSe2 allow the identification of its layer number and crystal orientation. Furthermore, PL measurements show the anisotropic optical emission intensity of the material with its bandgap increasing from 1.26 eV in the bulk to 1.32 eV in the monolayer. The study of the layer-number dependence of the Raman modes and the PL spectra reveals relatively weak van der Waal＇s interaction and two-dimensional （2D） quantum confinement in the atomically thin ReSe2. The experimental observation of the intriguing anisotropic interlayer interaction and tunable optical transition in monolayer and multilayer ReSe2 establishes the foundation for further exploration of this material in the development of anisotropic optoelectronic devices functioning in the near-infrared spectrum, which is important for many applications in optical communication and infrared sensing,

Highly sensitive phototransistors based on twodimensional GaTe nanosheets with direct bandgap

Highly sensitive phototransistors based on two-dimensional （2D） GaTe nanosheet have been demonstrated. The performance （photoresponsivity, detectivity） of the GaTe nanosheet phototransistor can be efficiently adjusted by using the applied gate voltage. The devices exhibit an ultrahigh photoresponsivity of 274.3 AW^-1. The detectivity of 2D GaTe devices is -10^12 Jones, which surpasses that of currently-exploited InGaAs photodetectors （10^11-10^12 Jones）. To reveal the origin of the enhanced photocurrent in GaTe nanosheets, theoretical modeling of the electronic structures was performed to show that GaTe nanosheets also have a direct bandgap structure, which contributes to the promotion of photon absorption and generation of excitons. This work shows that GaTe nanosheets are promising materials for high performance photodetectors.

Measuring bulk and surface acoustic modes in diamond by angle-resolved Brillouin spectroscopy

The acoustic modes of diamond are not only of profound significance for studying its thermal conductivity, mechanical properties, and optical properties, but also play a definite role in the performance of high-frequency and high-power acoustic wave devices. Here, we report on the bulk acoustic waves(BAWs) and surface acoustic waves(SAWs) of single-crystal diamond using angle-resolved Brillouin light scattering(BLS) spectroscopy. We identify two high-speed surface skimming bulk waves(SSBW) with acoustic velocities of 1.277×10^(6) and 1.727×10^(6) cm/s, respectively. Furthermore, we obtain the relationship between the velocity of arbitrary BAWs and that of BAWs propagating along the high-symmetric axis at different incident angles. In the community of diamond-based acoustic studies, our results may provide a valuable reference for fundamental research and device engineering.